Project Summary/Abstract Candidate: This K01 is submitted by Dr. del Pino, Associate Professor, from Charles R. Drew University of Medicine and Science (CDU). This proposal is the next step in his transition from philosophy to public health research. He seeks to reduce HIV disparities among Latino men who have sex with men (MSM) by analyzing family support data from three prospective cohort studies in Los Angeles and Chicago and by conducting formative research to leverage the siblings of Latino MSM in an HIV biomedical prevention intervention. He has published qualitative and quantitative papers on family support, substance use, and HIV. He is currently supported by the CDU Emerging Scholars Award and CRECD. Career Development and Training Plan: Dr. del Pino's mentoring team includes Dr. Steve Shoptaw (expert in substance use and biomedical interventions), Dr. Nina Harawa (expert in the development of culturally responsive HIV-prevention interventions for MSM of color), and Dr. Arun Karlamangla (expert in complex biostatistical data analysis and longitudinal clinical epidemiology research). The training goals (advanced biostatistics, families and stigma, and intervention development) will be achieved through coursework and individual tutorials with each mentor. He will have access to the UCLA CTSI (NCATS); UCLA CHIPTS (NIMH); and to AXIS, CDU's center for clinical and translational research resources and trainings (NIMHD). Research Plan: Despite the prevention and treatment efforts of the past 30 years, Latino MSM continue to be disproportionately impacted by HIV. Yet a powerful cultural source of motivation has been underutilized: the family. This project seeks to address HIV disparities by addressing gaps in our knowledge of (a) how family support affects the behaviors and health of Latino MSM over time and (b) how to engage siblings in the development and delivery of PrEP-use messages. Aim 1: Determine how family support and mental health affect the HIV-related behaviors (e.g., substance use, sexual risk) and HIV-related health (e.g., STI, HIV viral load) of Latino MSM over time. Hypothesis: Latino MSM with greater family support over time will report better HIV-related risk behaviors and health outcomes than Latino MSM who report little to no family support. Aim 2: Identify barriers and facilitators to engaging Latino MSM and siblings in HIV biomedical interventions. Aim 3: Develop and pilot test sibling-delivered messages to increase PrEP use in high-risk Latino MSM to gather feasibility and acceptability data and to refine the intervention processes and messages. Summary: The Career Development and Training Plan and the Research Plan will prepare Dr. del Pino to submit an R01 to test the efficacy and effectiveness of a culturally-specific, sibling-based intervention to reduce HIV disparities among Latino MSM. His mentorship team has the required expertise and established record of mentoring junior researchers to ensure that he becomes an independently-funded investigator.